Improvement method for water conservancy and hydropower high-pressure-difference low-back-pressure energy dissipation valve structure

Abstract

According to the water conservancy and hydropower high-pressure-difference low-back-pressure energy dissipation valve structure improvement method, flow and flow resistance characteristic models of a hedging type energy dissipation valve are established, numerical simulation analysis is conducted on an internal flow field of the energy dissipation valve, physical modeling is conducted on the energy dissipation valve, and non-structural and structured grids are adopted for grid division; the method comprises the following steps of: modeling an internal flow field of the opposite-flushing type energy dissipation valve under low back pressure, analyzing flow and flow resistance characteristics of two forms of energy dissipation valves by adopting physical models of a single-layer opposite-flushing type energy dissipation valve and a double-layer opposite-flushing type energy dissipation valve respectively, extracting flow field and energy dissipation characteristics of the single-layer energy dissipation valve and the double-layer energy dissipation valve, analyzing opening and closing dynamic processes of the double-layer energy dissipation valve on the basis of Pumplinx, and calculating the flow field and energy dissipation characteristics of the double-layer opposite-flushing type energy dissipation valve. The flow change process is analyzed, modeling is conducted on the single-layer energy dissipation valve under the working conditions of high pressure difference and low back pressure, and cavitation of the wall face of a round hole of a flow field of the single-layer energy dissipation valve is analyzed; a double-layer hedging type structure is improved, the energy dissipation valve capable of efficiently and stably working under the working conditions of high pressure difference and low back pressure is designed after improvement, and the energy dissipation valve has good reliability and safety.

Description

Technical Field

[0001] The present application relates to a fault diagnosis algorithm for a hydropower distribution transformer, and in particular to a method for improving the structure of a high-pressure difference and low-back-pressure energy dissipation valve for water conservancy and hydropower, belonging to the technical field of fault diagnosis for distribution transformers. Background Art

[0002] Energy dissipation valve is an important component in the pipeline system and is widely used in important water conservancy and hydropower projects such as long-distance water transmission and water diversion. The energy dissipation performance of the energy dissipation valve is directly related to the stability of the entire water transmission system. When designing an energy dissipation valve, the hydraulic characteristics should be considered mainly. However, in the past, engineers focused on structural design when designing energy dissipation valves, and paid less attention to hydraulic characteristics. The existing technology generally uses CFD technology to design valves. Its emergence provides a tool and means for studying the hydraulic characteristics of energy dissipation valves; however, when designing energy dissipation valves, the existing technology considers more about the mechanical structure and rarely considers the hydraulic characteristics of the valve. It is of great significance to optimize and improve the application of energy dissipation valves in engineering based on the hydraulic characteristics of the valve.

[0003] Energy dissipation valve is a type of regulating valve, mainly used to reduce pressure and adjust flow, and regulating valve is a type of valve. The role of regulating valve in fluid delivery pipeline is to adjust the system resistance. Its working principle is to change the resistance to water flow by changing the resistance coefficient of throttling components, thereby achieving the goal of regulating flow and reducing pressure. The counter-pressure energy dissipation valve mainly dissipates energy and reduces pressure to achieve the purpose of regulating flow and pressure. The indicators of the inherent performance of the regulating valve mainly include resistance characteristics and flow characteristics.

[0004] The counter-pressure energy dissipation valve is generally composed of two pipes of different diameters (valve core sleeve and outer tube), in which a plurality of vertical circular holes are arranged on the circumference of the small diameter inner tube, i.e., the valve core sleeve. When the water enters the energy dissipation valve and fills the space between the valve core sleeve and the outer tube, the water will flow into the valve core sleeve through the circular holes arranged on the circumference of the valve core sleeve, and then flow in the direction of water delivery. Due to the existence of the circular holes on the circumference of the valve core sleeve, the magnitude and direction of the fluid flow velocity change greatly. When entering the valve core sleeve through the circular holes on the circumference of the valve core sleeve, the high-speed fluids strongly collide with each other, and the change in local area becomes smaller, which also leads to head loss; after passing through the energy dissipation valve, it continues to flow in the downstream direction, and the settings of the valve core sleeve circular hole empty diameter, the number of circular holes, the valve core sleeve arrangement, etc. will affect the energy dissipation characteristics of this energy dissipation valve.

[0005] The problems that need to be solved by the high-pressure differential and low-back-pressure energy dissipation valve in the prior art and the key technical difficulties of this application include:

[0006] (1) The energy dissipation valve is an indispensable component in the engineering water supply system. It is also a component that has a greater impact on the system if problems occur. However, in the actual application process of high pressure difference and low back pressure, the selection and structural design of the energy dissipation valve are very difficult, and the energy dissipation effect is difficult to guarantee. As an energy dissipation component, the energy dissipation valve is the source of the system vibration noise. The unreasonable structure of the energy dissipation valve makes it difficult to control the noise. Because a specific energy dissipation valve has specific energy dissipation and flow characteristics, and the valve form is relatively fixed, the existing technology is difficult to fully match the requirements of the system. The flow and energy dissipation characteristics of the energy dissipation valve do not match the needs of the system. In order to solve these problems, the energy dissipation valve must be improved to develop in the direction of standardization and precision. However, the existing technology has not conducted in-depth research on the internal flow field of the energy dissipation valve, the mechanism of cavitation and vibration of the energy dissipation valve, and the protection method. It is impossible to improve the energy dissipation valve in a targeted manner, resulting in the energy dissipation valve being unable to operate stably, the energy dissipation effect being poor, and cavitation problems occurring under high pressure difference and low back pressure.

[0007] (2) In order to meet the pressure and flow requirements of long-distance water supply projects, it is necessary to install energy dissipation devices, control valves and other pipeline protection devices. Energy dissipation valves play a very important role in the flow regulation of water supply systems. However, the performance of energy dissipation valves in the existing technology has defects, resulting in instability in long-distance water supply systems. The existing technology does not conduct in-depth analysis of the internal structure of the counter-type energy dissipation valve, lacks flow field simulation and result analysis of the counter-type energy dissipation valve, and cannot clearly analyze the internal flow characteristics of the energy dissipation valve. It lacks computational fluid dynamics (CFD) methods, has not studied the distribution of the flow field of the counter-type energy dissipation valve under low back pressure, has not analyzed the flow performance of the single-layer counter-type energy dissipation valve and the double-layer counter-type energy dissipation valve, and the influence of the double-layer valve core on the energy dissipation performance of the energy dissipation valve. There is a lack of flow field analysis of the two dynamic processes of opening and closing of the double-layer counter-type energy dissipation valve, and has not analyzed the flow fields of single-layer and double-layer counter-type energy dissipation valves under high pressure difference and low back pressure conditions. There is also a lack of improvement on the structure of the energy dissipation valve, and a lack of an energy dissipation valve that can work efficiently and stably under high pressure difference and low back pressure conditions.

[0008] (3) The prior art lacks the flow and flow resistance characteristic model of the energy dissipation valve, does not establish the physical and flow basin model of the counter-pressure energy dissipation valve, does not mesh the flow basin model, and does not perform static and dynamic numerical modeling on the meshed single-layer and double-layer energy dissipation valves; lacks modeling and dynamic analysis of the energy dissipation valve, and is unable to analyze the flow and flow resistance characteristics of the two types of energy dissipation valves, does not extract the flow field and energy dissipation characteristics of the single-layer and double-layer energy dissipation valves, lacks the analysis of the opening and closing dynamic process of the double-layer energy dissipation valve based on Pumplinx, and is unable to analyze its flow change process. It lacks modeling of the single-layer energy dissipation valve under high pressure difference and low back pressure conditions, and is unable to analyze the cavitation on the circular hole wall of its flow field, and is unable to solve the cavitation problem of the single-layer energy dissipation valve under this condition through structural improvement. As a result, the energy dissipation valve of the prior art cannot be applied to the working conditions of high pressure difference and low back pressure, and its reliability, safety, and economy are poor, and the energy dissipation effect cannot meet the requirements. Summary of the invention

[0009] This application establishes the flow and flow resistance characteristic model of the counter-pressure energy dissipation valve, conducts numerical simulation analysis on the internal flow field of the energy dissipation valve from the hydraulic perspective of the energy dissipation valve based on Fluent software, and uses Pro / E modeling software to perform physical modeling of the energy dissipation valve. CFD divides its grid, and the grid division adopts unstructured and structured grids. The internal flow field of the counter-impact energy dissipation valve is modeled under low back pressure. The physical models of single-layer and double-layer counter-impact energy dissipation valves are respectively adopted to analyze the flow and flow resistance characteristics of the two forms of energy dissipation valves, and the flow field and energy dissipation characteristics of the single-layer and double-layer energy dissipation valves are extracted. The opening and closing dynamic process of the double-layer energy dissipation valve is analyzed based on Pumplinx, and its flow change process is analyzed. The single-layer energy dissipation valve is modeled under high pressure difference and low back pressure conditions, and the circular hole wall surface of its flow field is analyzed to have cavitation; the double-layer counter-impact structure is improved. Compared with the single-layer energy dissipation valve, the energy dissipation and anti-cavitation performance of the double-layer improved structure are enhanced. After the improvement, an energy dissipation valve that can work efficiently and stably under high pressure difference and low back pressure conditions is designed, which has good reliability and safety.

[0010] In order to achieve the above technical effects, the technical solutions adopted in this application are as follows:

[0011] The structural improvement method of the high-pressure difference and low back pressure energy dissipation valve of water conservancy and hydropower is to establish the flow and flow resistance characteristic model of the counter-type energy dissipation valve, and conduct numerical simulation analysis on the internal flow field of the energy dissipation valve from the hydraulic perspective of the energy dissipation valve based on Fluent software. The energy dissipation valve is physically modeled using Pro / E modeling software, and its grid is divided using ICEM CFD. The grid division adopts unstructured and structured grids. The internal flow field of the counter-type energy dissipation valve is modeled under low back pressure. The physical models of single-layer and double-layer counter-type energy dissipation valves are respectively used to analyze the flow and flow resistance characteristics of the two forms of energy dissipation valves, and the flow field and energy dissipation characteristics of single-layer and double-layer energy dissipation valves are extracted. The opening and closing dynamic process of the double-layer energy dissipation valve is analyzed based on Pumplinx, and its flow change process is analyzed. The single-layer energy dissipation valve is modeled under high pressure difference and low back pressure conditions, and the circular hole wall of its flow field is analyzed to have cavitation. The double-layer counter-type structure is improved, and the energy dissipation and anti-cavitation performance of the double-layer improved structure are enhanced compared with the single-layer energy dissipation valve.

[0012] A. Flow and flow resistance characteristic model of energy dissipation valve: The physical and flow domain model of DN2400 counter-impact energy dissipation valve is established through Pro / E, the flow domain model is meshed, static numerical modeling is performed on the meshed single-layer and double-layer DN2400 energy dissipation valve, and meshing is performed on the flow domain model of the double-layer counter-impact energy dissipation valve and dynamic numerical modeling of the valve opening and closing process is performed;

[0013] Modeling and dynamic analysis of B energy dissipation valve: First, a static model is established: the flow of a single-layer energy dissipation valve changes linearly with the increase of the opening. When the water flows through the energy dissipation valve, a collision area is formed in the valve core sleeve. There is a vortex in the front end of the valve core sleeve, and a vortex is formed in the area near the pipe wall behind the valve. The collision and vortex area dissipate energy, and the high-speed flow area is concentrated in the center of the valve core sleeve; the flow of a double-layer energy dissipation valve gradually slows down with the increase of the opening. After passing through the double-layer valve core and throttling twice with circular holes, the water flows in the inner layer of the valve core to form a collision energy dissipation, and then forms a central area flow velocity zone to flow downstream. The double-layer energy dissipation valve is more evenly distributed than the single-layer flow field at each opening, and the maximum flow rate is small; second, a dynamic model is established: during the closing and opening process of the double-layer energy dissipation valve, the flow through the valve changes linearly in a step-like manner with the increase of the opening, but the flow change rate gradually decreases;

[0014] C Modeling improvement of energy dissipation valve under high pressure difference and low back pressure: The double-layer counter-pressure energy dissipation valve operates stably under high pressure difference and low back pressure conditions, and the cavitation problem of the single-layer energy dissipation valve under this condition is solved through structural improvement.

[0015] Preferably, the energy dissipation valve flow rate regulation method is: the net inflow fluid mass through the fluid control surface of a section of the pipeline in unit time is equal to the increase in the control body including the fluid mass, and the continuity equation on the pressure pipeline is expressed as follows:

[0016] ρ1=ρ1;v1A1=v2A2=Q=Constant Formula 1

[0017] In the above formula, A represents the cross-sectional area of ​​the water pipeline, v is the average flow velocity of the pipeline, and ρ represents the density, which is the volume flow rate of the fluid passing through the cross section per unit time m 3 / s, considering the energy loss, it can be expressed as follows:

[0018]

[0019] Where, subscript 1 is the section before the energy dissipation device valve, subscript 2 is the section after the energy dissipation device valve, v1 and v2 are the average velocity of the fluid flow at the section, in units of m / s and h f is the head loss between the two sections, unit is m, and α is the fluid kinetic energy correction coefficient.

[0020] The pipe diameter and cross-sectional area before and after the energy dissipation valve are the same, so the flow rate before and after the energy dissipation valve is assumed to be v, and the energy loss of the incompressible viscous fluid after passing through the energy dissipation valve is expressed as:

[0021]

[0022] h f It can also be expressed as flow velocity and resistance coefficient, and its mathematical relationship is:

[0023]

[0024] Combined with the continuity equation v = Q / A, the flow equation of the energy dissipation valve is obtained as follows:

[0025]

[0026] Where the flow area A is in cm 2 , pressure before energy dissipation valve p1, pressure after energy dissipation valve p2, fluid density ρ, unit g / cm 3 , (p1-p2) is the pressure difference before and after the energy dissipation valve. When the flow area A of the energy dissipation valve is constant and the pressure difference (p1-p2) before and after the energy dissipation valve is unchanged, the flow rate Q increases as the resistance coefficient ξ decreases. The energy dissipation valve changes the valve resistance coefficient by changing the opening and layout to achieve energy dissipation and flow regulation.

[0027] Preferably, the characteristic factor of the energy dissipation valve is based on the flow coefficient, and is:

[0028]

[0029] get:

[0030]

[0031] N is a dimensionless coefficient. In the International System of Units (SI), the flow coefficient K is v It is defined as: the flow rate of water at room temperature passing through the energy dissipation valve within 1 hour under a pressure difference of 0.1MPa;

[0032]

[0033] Q represents the flow rate of the energy dissipation valve, in m 3 / h, △P represents the inlet and outlet pressure difference, the unit is 0.1MPa, ρ=1;

[0034] The flow resistance coefficient of the energy dissipation valve is a dimensionless quantity:

[0035]

[0036] in: h j =h w -h j , Q represents the flow rate through the valve, v represents the velocity of the fluid in the pipe, and h j Indicates the head loss through the valve, h w represents the total head loss, h f represents the head loss along the pipeline, λ represents the head loss coefficient along the pipeline, D represents the pipeline diameter, and L represents the distance between the valve and the pressure measuring tube.

[0037] Preferably, the performance prediction of the energy dissipation valve model is:

[0038] 1- Single-layer flow characteristics and flow resistance coefficient: DN2400 single-layer valve core of the energy dissipation valve with 5 different openings, analyze the flow change law of the energy dissipation valve, obtain the flow and resistance coefficient of the single-layer energy dissipation valve at different openings, record the flow value, calculate the flow coefficient of the valve, and summarize the results; in the process of valve opening, the flow resistance coefficient is very large at the beginning, and the flow resistance coefficient is reduced to 290 when the opening is 0.6. At the beginning, the flow resistance coefficient decreases rapidly. When the opening is large, the increase in the opening has little effect on the flow change. When fully opened, the flow resistance coefficient is still around 110. When fully opened, the energy dissipation effect of the energy dissipation valve is also more obvious;

[0039] 2-Double-layer flow characteristics and flow resistance coefficient: DN2400 counter-pressure energy dissipation valve is between the linear regulation characteristics and the quick-opening regulation characteristics during use. The flow through the counter-pressure energy dissipation valve increases linearly with the increase of the valve opening when the valve is opened, but the flow changes greatly, which is close to the quick-opening flow characteristics; after the opening is 0.3, the flow no longer changes linearly with the valve opening, and as the opening increases, the flow changes with the opening decreases; after the opening reaches 0.4, the relative speed of the flow change decreases significantly, and the flow changes with the opening as the opening approaches a larger value. The smaller the change in the degree, the flow regulation ability is not as strong as when it is close to full opening when it is small; in the process of valve opening, the flow resistance coefficient is very large at the beginning of opening, and the flow resistance coefficient is reduced to 161.68 when the opening is 0.6. The flow resistance coefficient of the valve decreases rapidly at the beginning of the valve opening process. After the opening reaches 0.6, the flow resistance coefficient gradually decreases with the change of the opening, that is, at a large opening, the increase in the opening has little effect on the flow change. When fully open, the flow resistance coefficient is still around 113. When fully open, the energy dissipation effect of the energy dissipation valve is more obvious.

[0040] Preferably, the dynamic process model of opening and closing of the energy dissipation valve is established and the parameters are set: the original model at the opening degree of 0.6 is modified in Pro / E, and the valve area is divided into four parts, namely, the part outside the internal valve core movement valve out, the internal valve core movement part valve mid, the front area of ​​the inner valve core movement valve up and the rear area of ​​the inner valve core movement valve down, and then the valve model with divided areas is saved as .stl file type, and is exported separately in four parts to obtain a physical model for dynamic simulation;

[0041] Import the obtained double-layer opposed energy dissipation valve .stl type physical model into Pumplinx, and then divide and name the faces of each area in Pumplinx, use the Split by Angle item in Split / Combine Geometry or Grid, and use appropriate angles to divide the faces of each area separately, so that the faces of each area are divided into the required faces, and other unnecessary faces are appropriately merged. After the required faces of each area are obtained, mesh each area separately; Mesh setting of the inner valve core movement area: Set the mesh of the valve up area under the spoolvalve model for division, bring the cylinder, valve and end faces in the valve up into the sliding valve model respectively, and then divide the mesh size, and set the minimum mesh to 0.0008; then set the mesh of the valve down area, use the structured mesh Template Mesh for division, and use the sliding valve module boundary setting in the subsequent boundary setting; then set the mesh division of the valve mid area, use the general mesh division Mesher, the minimum grid is set to 0.0008, and the boundary conditions are set using the sliding valve module boundary conditions; the setting of other static grids of the valve also uses the General Mesher module, and the minimum grid size is also set to 0.0008; the inlet and outlet pipe sections are divided using the structured grid Template Mesh. Through the above settings, the volume grid and surface grid of each area are obtained.

[0042] Set the interaction surface and boundary conditions of the regional grid body and the valve core motion parameters. The interaction surface settings are as follows: the contact surface between the inlet pipe and the inlet of the valve is set as an interaction surface, the contact surface between the outlet of the valve and the outlet pipe is set as an interaction surface, the end surface of the valve down is set as a contact surface with the static part of the valve, the cylinder surface of the spool valve, valve mid and valvedown is set as a contact surface with the static part of the valve, the end surface of the valve mid is set as an interaction surface with the valve surface of the valve down, and a certain pipe section is set before and after the valve inlet. The inlet of the inlet pipe section and the outlet of the outlet pipe section are set as pressure boundary conditions, and the pressure difference is about 1m head; the dynamic valve core is set as follows, the valve surface and cylinder surface of the valve down, valve mid and spool valve are set as the valve surface and cylinder surface of the sliding valve module respectively, and the valve down and spool The end surface of the valve is set to the end surface of the sliding valve module, and the other surfaces remain the default wall surfaces; the movement mode of the inner valve core is a dynamic process of uniform opening and closing with a speed of 0.068m / s, and the valve opening and closing time is 10s.

[0043] Preferably, the dynamic process analysis of the energy dissipation valve opening is as follows: firstly, a physical model is established and imported into Pumplinx; then, the imported model is divided into surfaces and the sliding valve model is imported; then, the divided surface model is meshed; finally, the boundary conditions are set and the movement mode of the valve core sleeve is set;

[0044] The energy dissipation valve opens at a uniform speed of 0.068m / s. When the double-layer offset energy dissipation valve is closed, the pressure before the inner valve core is constant and the flow is zero; the pressure after the inner valve core is constant and the flow is 0. During the valve opening process, the water flow begins to move under the action of pressure. At the beginning, the movement of the water flow is unstable. At the beginning, the flow increases rapidly with time. As time goes by, the rate of increase of the flow rate slows down. The trend of valve flow rate change with time is also the trend of valve flow rate change with opening degree, that is, the process of opening each hole basically changes linearly, but as the opening degree increases, the rate of change of flow rate in the process of opening each hole slows down.

[0045] Preferably, the model construction and boundary condition setting of the energy dissipation valve under high pressure difference and low back pressure: the energy dissipation effect of the single-layer energy dissipation valve must achieve the effect of high pressure difference, and the flow area of ​​the energy dissipation valve must be reduced to effectively throttle and strengthen the counter-pressure energy dissipation. The valve core sleeve diameter of the single-layer energy dissipation valve is 1600mm, and the outer and outer valve core sleeve diameters of the double-layer energy dissipation valve are 1600mm and 1000mm respectively. It is determined that the single-layer counter-pressure energy dissipation valve is set to 50 circular holes with a diameter of 90mm as the flow area, Arranged in 5 rows, 10 circular arrangements in each row, the double-layer energy dissipation valve adopts 60 circular holes with a diameter of 90mm in the outer layer, arranged in 5 rows, 12 circular arrangements in each row, and 80 circular holes with a diameter of 90mm in the inner layer, all arranged in 5 rows, 16 circular arrangements in each row, and 60 circular holes with a diameter of 85mm in the outer layer, arranged in 5 rows, 12 circular arrangements in each row, and 90 circular holes with a diameter of 90mm in the inner layer, all arranged in 5 rows, 18 circular arrangements in each row;

[0046] Use Pro / E to get the flow domain diagram of the two energy dissipation valves, then divide the grid in ICEM, and finally import the .mesh file into Fluent, then check whether the size scale of the model is in compliance, then set the turbulence model to the standard k-ε model, and then set the fluid medium to water, set the inlet and outlet of the two interface valve bodies, set the inlet of the inlet pipe and the outlet of the outlet pipe to pressure boundaries, the inlet pressure is the total pressure of about 100m head, and the outlet pressure is 5m head; the solution and discretization methods are set to the default settings, advanced steady-state calculation, do not add the cavitation model first, wait until the calculation is stable, and then add the cavitation model: first add the multiphase flow model, then add the gas-water fluid medium to the fluid medium, set the fluid water to the first phase, and set the second phase to the gas-water phase. There is a situation where the first phase is transformed into the second phase. The cavitation model is set to the default Schnerr-Sauer model, and the parameters under this model select the default settings.

[0047] Preferably, the flow field calculation of single-layer and double-layer energy dissipation valves: after numerical simulation by Fluent, the results are imported into CFD-Post for post-processing, and the result analysis includes: under the condition of high pressure difference and low back pressure, that is, the back pressure is 5m head, and the pressure difference is 95m, the place where cavitation is prone to occur is near the circular hole. The flow area of ​​the single-layer energy dissipation valve is very small, resulting in a large flow velocity at the circular hole, and the water flow has a large velocity head. The total head of low back pressure is constant, and the velocity head is very large, resulting in a decrease in the pressure head. When the pressure drops below the saturated vapor pressure of water at this temperature, liquid water will be converted into gaseous water, and cavitation will occur;

[0048] To reduce the cavitation part in the double-layer structure 1, it is necessary to reduce the flow velocity of the circular hole, so the double-layer structure 2 is established, the inner layer flow area increases, the outer layer flow area decreases, and the overall energy dissipation effect is the same;

[0049] The double-layer counter-impact energy dissipation valve with improved structure has a lower flow rate at the last row of circular holes in the inner valve core, and the pressure is above the vaporization pressure. The location with a higher flow rate in the improved structure of the energy dissipation valve appears at the circular holes in the outer valve core, and the back pressure of the circular holes in the outer valve core is relatively large, and there is no part where the pressure is lower than the vaporization pressure. At the same time, the energy dissipation capacity of the outer layer is improved, and there is a vortex in the area between the inner and outer layers, which improves the energy dissipation. After the water flows out of the circular holes on all sides in the inner layer area, counter-impact collision energy dissipation is formed;

[0050] From single-layer to double-layer structure 1 and then to double-layer structure 2 energy dissipation valve, the cavitation in the valve body changes from cavitation to partial cavitation and then to no cavitation, and the position and size of the cavitation also change from cavitation at the position of the circular hole used to cavitation at the position of part of the circular hole and then to no cavitation. The pit cavitation capacity of the energy dissipation valve after structural improvement is improved, and it is suitable for working conditions with high pressure difference and low back pressure.

[0051] Preferably, the flow field calculation of double-layer energy dissipation valves with different structures: by designing double-layer energy dissipation valves with different structures, the effect of the valve core sleeve diameter and the distance between the sleeves on energy dissipation is compared when the double-layer energy dissipation valves have the same flow area, that is, the number and size of the valve core circular holes are the same;

[0052] The structural design of the energy dissipation valve is as follows: the diameter of the outer valve core sleeve energy dissipation valve is the same as the diameter of the outer valve core sleeve of the energy dissipation valve, that is, the diameter is 1600mm, the diameter of the inner energy dissipation valve is changed to 1200mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers; the diameter of the inner energy dissipation valve is the same as the diameter of the above energy dissipation valve, that is, the diameter is 1600mm, the diameter of the valve core sleeve of the outer energy dissipation valve is changed to 2000mm and 2200mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers; the diameter of the outer energy dissipation valve is the same as the diameter of the inner valve core sleeve of the energy dissipation valve, that is, the diameter is 1000mm, the diameter of the inner energy dissipation valve is changed to 600mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers;

[0053] Under the condition of high pressure difference and low back pressure, that is, the back pressure is 5m head and the pressure difference is 95m, the difference in flow field and energy dissipation is analyzed: when the diameter of the inner valve core sleeve remains unchanged, changing the distance between the outer valve core and the inner valve core, that is, increasing the diameter of the outer valve core sleeve, has little effect on the energy dissipation effect of the energy dissipation valve; when the diameter of the outer valve core remains unchanged, changing the diameter of the inner valve core in a small range has little effect on the energy dissipation effect; but when the diameters of both the outer valve core and the inner valve core are reduced, the water flow counter-impact effect in the inner layer is obvious and the energy dissipation effect is enhanced.

[0054] Preferably, under the condition of high pressure difference and low back pressure, the flow field calculation of single-layer counter-pressure energy dissipation valve and double-layer counter-pressure energy dissipation valve is different. Under the same pressure boundary conditions and other settings at both ends, the flow rate of single-layer counter-pressure energy dissipation valve is 9.6m 3 / s, the flow rate of the double-layer counter-pressure energy dissipation valve is 9.3m3 / s, the energy dissipation effects of the two valves are basically the same, and the flow conditions are basically the same. Under this condition, cavitation occurs near the wall of the circular hole of the valve core of the single-layer offset energy dissipation valve, which is not conducive to the normal operation of the energy dissipation valve and is not suitable for this condition; compared with the single-layer offset energy dissipation valve, the double-layer offset energy dissipation valve of structure 1 completes energy dissipation and pressure reduction under this condition, but slight cavitation occurs in the valve body; the improved double-layer offset energy dissipation valve of structure 2 completes energy dissipation and pressure reduction under this condition, and no cavitation occurs in the valve body. Under the condition of high pressure difference and low back pressure, the double-layer energy dissipation valve with improved structure is better than the single-layer energy dissipation valve.

[0055] Compared with the prior art, the innovations and advantages of this application are:

[0056] (1) This application establishes a flow and flow resistance characteristic model of the counter-pressure energy dissipation valve, performs numerical simulation analysis on the internal flow field of the energy dissipation valve from the hydraulic perspective of the energy dissipation valve based on Fluent software, and uses Pro / E modeling software to perform physical modeling of the energy dissipation valve. CFD divides its grid, and the grid division adopts unstructured and structured grids. The internal flow field of the counter-impact energy dissipation valve is modeled under low back pressure. The physical models of single-layer and double-layer counter-impact energy dissipation valves are respectively adopted to analyze the flow and flow resistance characteristics of the two forms of energy dissipation valves, and the flow field and energy dissipation characteristics of the single-layer and double-layer energy dissipation valves are extracted. The opening and closing dynamic process of the double-layer energy dissipation valve is analyzed based on Pumplinx, and its flow change process is analyzed. The single-layer energy dissipation valve is modeled under high pressure difference and low back pressure conditions, and the circular hole wall surface of its flow field is analyzed to have cavitation; the double-layer counter-impact structure is improved. Compared with the single-layer energy dissipation valve, the energy dissipation and anti-cavitation performance of the double-layer improved structure are enhanced. After the improvement, an energy dissipation valve that can work efficiently and stably under high pressure difference and low back pressure conditions is designed, which has good reliability and safety.

[0057] (2) This application proposes a flow and flow resistance characteristic model of the energy dissipation valve, establishes the physical and flow basin model of the DN2400 counter-impact energy dissipation valve through Pro / E, meshes the flow basin model, performs static numerical modeling on the meshed single-layer and double-layer DN2400 energy dissipation valves, and meshes the flow basin model of the double-layer counter-impact energy dissipation valve and performs dynamic numerical modeling of the valve opening and closing process; This application realizes the modeling and dynamic analysis of the energy dissipation valve: First, a static model is established: the flow of the single-layer energy dissipation valve changes linearly with the increase of the opening degree. When the water flows through the energy dissipation valve, a counter-impact collision area is formed in the valve core sleeve. There is a vortex at the front end of the valve core sleeve, and a vortex is formed in the area near the pipe wall behind the valve. The counter-impact collision and vortex area dissipate energy, and the high-speed flow area is concentrated in the valve core. The center area of ​​the sleeve; the flow rate of the double-layer energy dissipation valve gradually slows down with the increase of the opening. After the water flows through the double-layer valve core and is throttled by the circular holes twice, it forms a counter-energy dissipation in the inner area of ​​the inner valve core, and then forms a flow velocity zone in the central area to flow downstream. The double-layer energy dissipation valve is more evenly distributed than the single-layer flow field at each opening, and the maximum flow velocity is small; second, a dynamic model is established: during the closing and opening process of the double-layer energy dissipation valve, the flow rate through the valve changes linearly in a step-like manner with the increase of the opening, but the flow rate change rate gradually decreases. Through in-depth research on the internal flow field of the energy dissipation valve, the mechanism of cavitation and vibration of the energy dissipation valve, and the protection methods, the energy dissipation valve is improved in a targeted manner. After the improvement, the energy dissipation valve operates stably, has a good energy dissipation effect, and will not have cavitation problems under high pressure difference and low back pressure.

[0058] (3) This application proposes an improved modeling method for energy dissipation valves under high pressure difference and low back pressure. Based on the standard k-model, the Fluent software is used to perform numerical simulation on single-layer and double-layer DN2400 counter-pressure energy dissipation valves. Through the calculation results, its flow characteristics, flow resistance characteristics and other performance are predicted, and the characteristics of its internal flow field are analyzed; then Pumplinx is used to analyze the dynamic changes of the internal flow field of the valve during the opening and closing process of the double-layer valve core valve; finally, the flow fields of single-layer and double-layer counter-pressure energy dissipation valves under high pressure difference and low back pressure are analyzed and compared. The designed double-layer counter-pressure energy dissipation valve operates stably under high pressure difference and low back pressure conditions. The cavitation problem of the single-layer energy dissipation valve under this condition is solved through structural improvement. It is suitable for high pressure difference and low back pressure conditions, has good economic performance, and the energy dissipation effect meets the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a comparison chart of numerical simulation flow values ​​of DN2400 counter-pressure energy dissipation valve.

[0060] Figure 2 It is a comparison chart of flow resistance coefficients of the counter-impedance energy dissipation valve at various opening degrees.

[0061] Figure 3 It is the flow resistance characteristic curve of DN2400 counter-pressure energy dissipation valve.

[0062] Figure 4 It is a comparison diagram of the single-layer and double-layer energy dissipation valve structures.

[0063] Figure 5 It is the streamline diagram and pressure distribution diagram of the third empty cross section of the single-layer energy dissipation valve.

[0064] Figure 6 It is the flow velocity distribution diagram of single-layer counter-impact energy dissipation valve.

[0065] Figure 7 It is the streamline diagram and pressure distribution diagram of the last empty cross section of the double-layer energy dissipation valve.

[0066] Figure 8 It is the streamline diagram and pressure distribution diagram of the second emptying cross section of the double-layer energy dissipation valve.

[0067] Fig. 9 It is a gas phase volume distribution diagram of a double-layer structure 2 double-layer counter-impact energy dissipation valve.

[0068] Fig.10 This is the pressure distribution diagram of the double-layer counter-pressure energy dissipation valve under structure 2.

[0069] Fig.11 It is a comparison chart of parameters of different structural parts under low back pressure and high pressure difference working conditions. DETAILED DESCRIPTION

[0070] The following, in conjunction with the accompanying drawings, further describes the technical solution of the method for improving the structure of the water conservancy and hydropower high-pressure difference and low back-pressure energy dissipation valve provided in the present application, so that those skilled in the art can better understand the present application and implement it.

[0071] This application establishes a flow rate and flow resistance characteristic model of the counter-pressure energy dissipation valve, conducts a numerical simulation study on the internal flow field of the energy dissipation valve from the hydraulic perspective of the energy dissipation valve, and analyzes the flow conditions of the flow field.

[0072] (1) The energy dissipation valve was physically modeled using Pro / E modeling software, and its mesh was divided using ICEMCFD. The mesh division mainly used unstructured mesh and structured mesh.

[0073] (2) In the process of simulating the internal flow field of the opposed energy dissipation valve under low back pressure, the physical models of the single-layer opposed energy dissipation valve and the double-layer opposed energy dissipation valve were used respectively to analyze the flow and flow resistance characteristics of the two types of opposed energy dissipation valves, and the flow field characteristics and energy dissipation characteristics of the single-layer and double-layer opposed energy dissipation valves were summarized.

[0074] (3) Pumplinx was used to simulate and analyze the opening and closing dynamic processes of the double-layer opposed energy dissipation valve, mainly analyzing its flow change process.

[0075] (4) The single-layer counter-pressure energy dissipation valve was numerically simulated under high pressure difference and low back pressure conditions, and its flow field was analyzed. It was found that cavitation occurred on the wall of the circular hole. The double-layer counter-pressure energy dissipation valve was improved and the cavitation phenomenon was significantly reduced or even disappeared. This shows that the double-layer counter-pressure energy dissipation valve has better energy dissipation performance and anti-cavitation ability than the single-layer counter-pressure energy dissipation valve, and the improvement of the energy dissipation valve structure has been achieved.

[0076] 1. Flow rate and flow resistance characteristic model of energy dissipation valve

[0077] (I) Energy dissipation valve flow adjustment method

[0078] The energy dissipation of the energy dissipation valve is to change the form or structural parameters of the throttling element, thereby changing the resistance of the energy dissipation device to the fluid. The flow rate through the energy dissipation valve in the water supply system is determined based on the fluid dynamics relationship.

[0079] The net inflow mass of the fluid through the fluid control surface of a section of the pipeline per unit time is equal to the increase in the mass of the fluid contained in the control body. The continuity equation on the pressure pipeline is expressed as follows:

[0080] ρ1=ρ1;v1A1=v2A2=Q=Constant Formula 1

[0081] In the above formula, A represents the cross-sectional area of ​​the water pipeline, v is the average flow velocity of the pipeline, and ρ represents the density, which is the volume flow rate of the fluid passing through the cross section per unit time m 3 / s, considering the energy loss, it can be expressed as follows:

[0082]

[0083] Where, subscript 1 is the section before the energy dissipation device valve, subscript 2 is the section after the energy dissipation device valve, v1 and v2 are the average velocity of the fluid flow at the section, in units of m / s and h f is the head loss between the two sections, unit is m, and α is the fluid kinetic energy correction coefficient.

[0084] The pipe diameter and cross-sectional area before and after the energy dissipation valve are the same, so the flow rate before and after the energy dissipation valve is assumed to be v, and the energy loss of the incompressible viscous fluid after passing through the energy dissipation valve is expressed as:

[0085]

[0086] h f It can also be expressed as flow velocity and resistance coefficient, and its mathematical relationship is:

[0087]

[0088] Combined with the continuity equation v = Q / A, the flow equation of the energy dissipation valve is obtained as follows:

[0089]

[0090] Where the flow area A is in cm 2 , pressure before energy dissipation valve p1, pressure after energy dissipation valve p2, fluid density ρ, unit g / cm 3 , (p1-p2) is the pressure difference before and after the energy dissipation valve. When the flow area A of the energy dissipation valve is constant and the pressure difference (p1-p2) before and after the energy dissipation valve is unchanged, the flow rate Q increases as the resistance coefficient ξ decreases. The energy dissipation valve changes the valve resistance coefficient by changing the opening and layout to achieve energy dissipation and flow regulation.

[0091] (II) Flow characteristics of energy dissipation valve

[0092] The pressure difference between the two ends of the valve will change with the change of the working conditions of the water delivery system, causing the ideal flow characteristic curve to be distorted. The relationship between the ideal flow characteristic and the working flow characteristic is expressed as:

[0093]

[0094] q / Q is the relative value of flow rate, l / L is the relative value of stroke.

[0095] (III) Characteristic factors of energy dissipation valve

[0096] Based on the flow coefficient, let:

[0097]

[0098] get:

[0099]

[0100] N is a dimensionless coefficient. In the International System of Units (SI), the flow coefficient K is v It is defined as: the flow rate of water at room temperature passing through the energy dissipation valve within 1 hour under a pressure difference of 0.1MPa;

[0101]

[0102] Q represents the flow rate of the energy dissipation valve, in m 3 / h, △P represents the inlet and outlet pressure difference, the unit is 0.1MPa, ρ=1;

[0103] The flow resistance coefficient of the energy dissipation valve is a dimensionless quantity:

[0104]

[0105] in: h j =h w -h f , Q represents the flow rate through the valve, v represents the velocity of the fluid in the pipe, and hj Indicates the head loss through the valve, h w represents the total head loss, h f represents the head loss along the pipeline, λ represents the head loss coefficient along the pipeline, D represents the pipeline diameter, and L represents the distance between the valve and the pressure measuring tube.

[0106] 2. Modeling and dynamic analysis of energy dissipation valve

[0107] The physical model of the opposed energy dissipation valve is established by using Pro / E, and the physical model is converted into a mesh model by using ICEM. The boundary conditions and numerical solution method solver settings are set in Fluent. The flow and resistance changes of the opposed energy dissipation valve at different openings are analyzed, and the flow and resistance characteristic curves are arranged and plotted. The flow changes through the energy dissipation valve during the dynamic process of opening and closing of the double-layer DN2400 opposed energy dissipation valve are analyzed.

[0108] (I) Energy dissipation valve model performance prediction

[0109] 1. Single-layer flow characteristics and flow resistance coefficient

[0110] The single-layer valve core of the DN2400 offset energy dissipation valve is analyzed at 5 different openings to analyze the flow rate change law of the energy dissipation valve, obtain the flow rate and resistance coefficient of the single-layer energy dissipation valve at different openings, record the flow value, calculate the flow coefficient of the valve, and summarize the results as follows: Figure 1 . Plot the changes in flow opening and flow coefficient into a curve.

[0111] Based on the relationship between flow rate and opening at 5 different openings, the flow resistance coefficient is calculated. The calculation results of opening and flow resistance coefficient are summarized in Figure 2 The fitted flow resistance characteristic curve is as follows Figure 3 .

[0112] During the process of valve opening, the flow resistance coefficient is very large at the beginning. When the opening is 0.6, the flow resistance coefficient decreases to 290. At the beginning, the flow resistance coefficient decreases rapidly. When the opening is large, the increase in the opening has little effect on the flow change. When fully open, the flow resistance coefficient is still around 110. When fully open, the energy dissipation effect of the energy dissipation valve is also obvious.

[0113] 2. Double-layer flow characteristics and flow resistance coefficient

[0114] The DN2400 counter-pressure energy dissipation valve is between the linear regulation characteristics and the quick-opening regulation characteristics during use. The flow through the counter-pressure energy dissipation valve increases linearly with the increase of the valve opening when the valve is opened, but the flow rate changes greatly, which is close to the quick-opening flow characteristic. After the opening is 0.3, the flow rate no longer changes linearly with the valve opening, and the change of the flow rate with the opening becomes smaller as the opening increases. After the opening reaches 0.4, the relative speed of flow change decreases significantly. The closer to the larger the opening, the smaller the change of flow rate with the opening. When it is close to full opening, the flow regulation ability is not as strong as when it is at a small opening.

[0115] When the valve is opening, the flow resistance coefficient is very large at the beginning. When the opening is 0.6, the flow resistance coefficient is reduced to 161.68. When the valve is opening, the flow resistance coefficient decreases rapidly at the beginning. After the opening reaches 0.6, the flow resistance coefficient gradually decreases with the change of the opening. That is, when the opening is large, the increase of the opening has little effect on the flow change. When it is fully opened, the flow resistance coefficient is still around 113. When it is fully opened, the energy dissipation effect of the energy dissipation valve is more obvious.

[0116] (II) Calculation of dynamic process of opening and closing of energy dissipation valve

[0117] 1. Model establishment and parameter setting

[0118] In Pro / E, the original model at 0.6 opening was modified, and the valve area was divided into four parts, namely, valve out, the part outside the internal valve core movement, valve mid, the part of the internal valve core movement, valve up, the front area of ​​the inner valve core movement, and valve down, the rear area of ​​the inner valve core movement. Then the valve model with divided areas was saved as .stl file type, divided into four parts and exported separately to obtain the physical model for dynamic simulation.

[0119] Import the obtained double-layer opposed energy dissipation valve .stl type physical model into Pumplinx, and then divide and name the faces of each area in Pumplinx, use the Split by Angle item in Split / Combine Geometry or Grid, and use appropriate angles to divide the faces of each area separately, so that the faces of each area are divided into the required faces, and other unnecessary faces are appropriately merged. After the required faces of each area are obtained, mesh each area separately; Mesh setting of the inner valve core movement area: Set the mesh of the valve up area under the spoolvalve model for division, bring the cylinder, valve and end faces in the valve up into the sliding valve model respectively, and then divide the mesh size, and set the minimum mesh to 0.0008; then set the mesh of the valve down area, use the structured mesh Template Mesh for division, and use the sliding valve module boundary setting in the subsequent boundary setting; then set the mesh division of the valve mid area, use the general mesh division Mesher, the minimum grid is set to 0.0008, and the boundary conditions are set using the sliding valve module boundary conditions; the setting of other static grids of the valve also uses the General Mesher module, and the minimum grid size is also set to 0.0008; the inlet and outlet pipe sections are divided using the structured grid Template Mesh. Through the above settings, the volume grid and surface grid of each area are obtained.

[0120] Set the interaction surface and boundary conditions of the regional grid body and the valve core motion parameters. The interaction surface settings are as follows: the contact surface between the inlet pipe and the inlet of the valve is set as an interaction surface, the contact surface between the outlet of the valve and the outlet pipe is set as an interaction surface, the end surface of the valve down is set as a contact surface with the static part of the valve, the cylinder surface of the spool valve, valve mid and valvedown is set as a contact surface with the static part of the valve, the end surface of the valve mid is set as an interaction surface with the valve surface of the valve down, and a certain pipe section is set before and after the valve inlet. The inlet of the inlet pipe section and the outlet of the outlet pipe section are set as pressure boundary conditions, and the pressure difference is about 1m head; the dynamic valve core is set as follows, the valve surface and cylinder surface of the valve down, valve mid and spool valve are set as the valve surface and cylinder surface of the sliding valve module respectively, and the valve down and spool The end surface of the valve is set to the end surface of the sliding valve module, and the other surfaces remain the default wall surfaces; the movement mode of the inner valve core is a dynamic process of uniform opening and closing with a speed of 0.068m / s, and the valve opening and closing time is 10s.

[0121] 2. Analysis of the dynamic process of energy dissipation valve opening

[0122] First, a physical model is established and imported into Pumplinx; then the imported model is divided into surfaces and the sliding valve model is imported; then the divided model is meshed; finally, the boundary conditions are set and the movement mode of the valve core sleeve is set.

[0123] The energy dissipation valve opens at a uniform speed of 0.068m / s. When the double-layer offset energy dissipation valve is closed, the pressure before the inner valve core is constant and the flow is zero; the pressure after the inner valve core is constant (less than the pressure before the valve) and the flow is 0. During the valve opening process, the water flow begins to move under the action of pressure. At the beginning, the movement of the water flow is unstable. At the beginning, the flow increases rapidly with time. As time goes by, the rate of increase of the flow rate slows down with time. The trend of valve flow rate change with time is also the trend of valve flow rate change with opening degree, that is, the process of opening each hole basically changes linearly, but as the opening degree increases, the rate of change of flow rate in the process of opening each hole slows down.

[0124] (III) Dynamic analysis results of energy dissipation valve

[0125] Firstly, the physical model of the single-layer and double-layer valve core DN2400 offset energy dissipation valve is established, its flow field model is optimized, and the ICEM is used to divide the mesh. Finally, the flow field of the DN2400 offset energy dissipation valve at different openings is solved in Fluent, and the following is obtained:

[0126] (1) As the opening of the single-layer DN2400 offset energy dissipation valve increases, the fluid flow through the energy dissipation valve increases linearly, that is, the single-layer DN2400 offset energy dissipation valve has good linear regulation ability; as the opening of the double-layer DN2400 offset energy dissipation valve increases, the fluid flow through the energy dissipation valve increases faster at a small opening, and the increase rate gradually slows down at a large opening, that is, the double-layer DN2400 offset energy dissipation valve has a regulation ability close to the characteristics of the quick opening type;

[0127] (2) The flow field changes of single-layer and double-layer DN2400 offset energy dissipation valves at three different openings, large, medium and small, are analyzed. As the opening of the energy dissipation valve increases, the energy dissipation effect of the energy dissipation valve decreases. At a large opening (full opening), after the water flows through the circular hole of the valve core sleeve, the flow area is large at this time, and the high-speed area formed near the center of the valve has a large flow velocity. Correspondingly, the flow areas of medium opening (60% opening) and small opening (20% opening) are small, and the high-speed area near the center of the energy dissipation valve is not large. The smaller the opening, the better the energy dissipation effect. The double-layer energy dissipation valve achieves different energy dissipation effects by changing the flow area of ​​the inner valve core, and the flow area of ​​the outer valve core remains unchanged.

[0128] By establishing the physical model of the double-layer valve core DN2400 offset energy dissipation valve, its static and dynamic flow domain models are obtained by partitioning. The dynamic flow domain model is dynamically meshed using the sliding valve module, and other valve parts are meshed using ordinary formats. The dynamic changes of the flow rate of the double-layer valve core DN2400 offset energy dissipation valve during the opening and closing process are solved. During the uniform opening and closing of the energy dissipation valve, the flow rate through the valve changes linearly in a step-like manner with the opening degree, that is, the change rate of the flow rate gradually decreases with the increase of the opening degree during the opening of the valve, and the change rate of the flow rate gradually increases with the decrease of the opening degree during the closing process.

[0129] 3. Modeling improvement of energy dissipation valve under high pressure difference and low back pressure

[0130] (I) Model construction and boundary condition setting

[0131] To achieve the effect of high pressure difference in energy dissipation effect of single-layer energy dissipation valve, the flow area of ​​energy dissipation valve must be reduced, effective throttling and strengthening counter-energy dissipation. The valve core sleeve diameter of single-layer energy dissipation valve is 1600mm, and the outer and outer valve core sleeve diameters of double-layer energy dissipation valve are 1600mm and 1000mm respectively. It is determined that the single-layer counter-energy dissipation valve is set to 50 circular holes with a diameter of 90mm as the flow area, which are arranged in 5 rows, with 10 circular holes in each row. Its structure is as follows: Figure 4 (a) The double-layer energy dissipation valve has 60 circular holes with a diameter of 90 mm in the outer layer, arranged in 5 rows, with 12 circular holes in each row, and 80 circular holes with a diameter of 90 mm in the inner layer, all arranged in 5 rows, with 16 circular holes in each row, and 60 circular holes with a diameter of 85 mm in the outer layer, arranged in 5 rows, with 12 circular holes in each row, and 90 circular holes with a diameter of 90 mm in the inner layer, all arranged in 5 rows, with 18 circular holes in each row. Its structure is as follows: Figure 4 (b) and Figure 4 (c).

[0132] Use Pro / E to get the flow domain diagram of the two energy dissipation valves, then divide the grid in ICEM, and finally import the .mesh file into Fluent, then check whether the size scale of the model is in compliance, then set the turbulence model to the standard k-ε model, and then set the fluid medium to water, set the inlet and outlet of the two interface valve bodies, set the inlet of the inlet pipe and the outlet of the outlet pipe to pressure boundaries, the inlet pressure is the total pressure of about 100m head, and the outlet pressure is 5m head; the solution and discretization methods are set to the default settings, advanced steady-state calculation, do not add the cavitation model first, wait until the calculation is stable, and then add the cavitation model: first add the multiphase flow model, then add the gas-water fluid medium to the fluid medium, set the fluid water to the first phase, and set the second phase to the gas-water phase. There is a situation where the first phase is transformed into the second phase. The cavitation model is set to the default Schnerr-Sauer model, and the parameters under this model select the default settings.

[0133] (II) Flow field analysis and calculation of single-layer and double-layer energy dissipation valves

[0134] 1. Flow field calculation of single-layer and double-layer energy dissipation valves

[0135] After the Fluent numerical simulation, the results are imported into CFD-Post for post-processing. The result analysis includes:

[0136] Under the condition of high pressure difference and low back pressure, that is, the back pressure is 5m head, and the pressure difference is 95m, cavitation is likely to occur near the circular hole. The flow area of ​​the single-layer energy dissipation valve is very small, resulting in a large water flow velocity at the circular hole. The water flow has a large velocity head. The total head of low back pressure is certain, and the velocity head is very large, resulting in a decrease in pressure head. When the pressure drops below the saturated vapor pressure of water at that temperature, liquid water will be converted into gaseous water, and cavitation will occur.

[0137] The pressure near the side wall of the circular hole where cavitation occurs reaches the vaporization pressure. The flow velocity of the circular hole is very high, and the pressure near the side wall of the circular hole decreases, resulting in the occurrence of cavitation. Figure 5 It was found that the low-pressure area in the front row of circular holes is larger.

[0138] Figure 6The velocity distribution diagram of the single-layer counter-attack energy dissipation valve. The velocity at the position of the circular hole of the single-layer valve core sleeve is very large, reaching more than 37m / s, which is consistent with the position where cavitation occurs. The cavitation near the wall of the circular hole is the sharp increase of the local velocity, which causes the local pressure to drop below the saturated vapor pressure of water. Cavitation occurs near the wall of the circular hole. When the flow rate is large, the local pressure drops below the saturated vapor pressure of water. After the water flows out of the circular hole, the velocity decreases rapidly, and the cavitation disappears. Then the water forms a counter-attack collision near the center area of ​​the valve, and finally flows downstream. The mainstream area of ​​the water flow is concentrated in the center area of ​​the pipe.

[0139] When the back pressure is low, the gas phase appears near the circular hole with a very high flow rate. The flow rate through the circular hole cannot be too large, otherwise cavitation will occur. If a single-layer energy dissipation valve is used, cavitation will still occur. Therefore, a double-layer counter-pressure energy dissipation valve is used. After using the double layer, the pressure required to reduce each layer will become smaller, the area of ​​the circular hole will increase appropriately, and the flow rate will decrease compared to the single-layer flow rate, and cavitation will not occur.

[0140] from Figure 7 and Figure 8 It can be seen that the flow velocity at the last row of circular holes in the inner valve core is relatively large, and there is partial cavitation, while the flow velocity at the front row of circular holes is relatively low, and no cavitation occurs. The double layer undergoes two collision energy dissipations, that is, another energy dissipation between the inner and outer layers, and another energy dissipation after passing through the circular holes of the inner valve core. The flow velocity of the double layer is not as large as that of the single layer, but achieves the same energy dissipation.

[0141] At the position of the circular hole of the double-layer valve core sleeve, the flow velocity is still very high, reaching more than 30m / s locally, but not as high as the local flow velocity of the single-layer, indicating that the flow velocity is reduced, making the minimum pressure of the double-layer energy dissipation valve slightly lower than the saturated vapor pressure of water, and a small amount of cavitation occurs. The water flows through the circular hole of the outer valve core sleeve at a higher speed into the area between the two layers, and the flow velocity slows down. Then the flow velocity increases and passes through the circular hole of the inner valve core sleeve, and enters the internal area of ​​the inner valve core to form hedging energy dissipation. The flow velocity decreases rapidly, and then the water flow after the hedging gathers in the center area of ​​the valve and finally flows downstream.

[0142] To reduce the cavitation part in the double-layer structure 1, it is necessary to reduce the flow velocity of the circular hole, so the double-layer structure 2 is established, the inner layer flow area increases, the outer layer flow area decreases, and the overall energy dissipation effect is the same. Fig. 9 This is the gas phase volume distribution diagram of the double-layer structure 2 double-layer counter-pressure energy dissipation valve. No cavitation occurs in the energy dissipation valve under this working condition. The improved structure eliminates cavitation under high pressure difference and low back pressure working conditions.

[0143] In the double-layer counter-impact energy dissipation valve with improved structure, the flow velocity at the last row of circular holes in the inner valve core is reduced, and the pressure is above the vaporization pressure. The position with higher flow velocity in the energy dissipation valve with improved structure appears at the circular holes in the outer valve core. The back pressure of the circular holes in the outer valve core is relatively large, and there is no part with pressure lower than the vaporization pressure. At the same time, the energy dissipation capacity of the outer layer is improved, and there is vortex in the area between the inner and outer layers to improve energy dissipation. After the water flows out of the circular holes on the surrounding areas in the inner layer, counter-impact collision energy dissipation is formed.

[0144] Fig.10 This is the pressure distribution diagram of the double-layer counter-pressure energy dissipation valve under structure 2. The maximum flow rate occurs at the circular hole of the outer energy dissipation valve. The outer energy dissipation valve eliminates part of the energy, and the flow rate of the inner energy dissipation valve decreases. Corresponding to the pressure distribution, there is no pressure lower than the saturated vapor pressure. The energy dissipation valve reaches the working condition of high pressure difference and low back pressure, and no cavitation occurs.

[0145] From the flow field analysis results of the three structures of energy dissipation valves under the above high pressure difference and low back pressure conditions, it can be obtained that Fig.11 The flow rates under the three structures are basically the same, that is, the working conditions of the energy dissipation valves under the three structures are basically the same; from the single-layer to the double-layer structure 1 and then to the double-layer structure 2 energy dissipation valve, the cavitation in the valve body changes from cavitation to partial cavitation and then to no cavitation, and the position and size of the cavitation also change from cavitation at the position of the circular hole used to cavitation at the position of part of the circular hole and then to no cavitation. The pit cavitation capacity of the energy dissipation valve after the structural improvement is improved, and it is suitable for working conditions with high pressure difference and low back pressure.

[0146] 2. Flow field calculation of double-layer energy dissipation valves with different structures

[0147] By designing double-layer energy dissipation valves with different structures, the effects of the valve core sleeve diameter and the distance between the sleeves on energy dissipation are compared when the flow area is the same, that is, the number and size of the valve core circular holes are the same.

[0148] The structural design of the energy dissipation valve is as follows: the diameter of the outer valve core sleeve energy dissipation valve is the same as the diameter of the outer valve core sleeve of the energy dissipation valve, that is, the diameter is 1600mm, the diameter of the inner energy dissipation valve is changed to 1200mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers; the diameter of the inner energy dissipation valve is the same as the diameter of the above-mentioned energy dissipation valve, that is, the diameter is 1600mm, the diameter of the valve core sleeve of the outer energy dissipation valve is changed to 2000mm and 2200mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers; the diameter of the outer energy dissipation valve is the same as the diameter of the inner valve core sleeve of the energy dissipation valve, that is, the diameter is 1000mm, the diameter of the inner energy dissipation valve is changed to 600mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers.

[0149] Under the condition of high pressure difference and low back pressure, that is, the back pressure is 5m head and the pressure difference is 95m, the differences in flow field and energy dissipation are analyzed.

[0150] The double-layer counter-impact energy dissipation valve has an inner diameter of 1600mm and an outer diameter of 2000mm. The outer valve core sleeve diameter increases, the distance between the two layers remains unchanged, and the energy dissipation effect does not change much. However, after passing through the circular hole of the inner layer, the counter-impact energy dissipation effect between the water flows slows down. At the same time, there are also eddies in the area between the inner and outer layers, which also play a certain role in energy dissipation. After the water flows in the inner layer area come out from the circular holes around, the counter-impact collision energy dissipation is formed. Since the diameter of the inner layer is larger than before, after the water flows come out from the circular hole of the inner sleeve, they meet after a certain distance, and there is still a counter-impact effect, and the water flow counter-impact type has rotation.

[0151] For the double-layer counter-impact energy dissipation valve with an inner diameter of 1600mm and an outer diameter of 2200mm, after the diameter of the outer valve core sleeve increases, the distance between the two layers remains unchanged compared to the original, and the energy dissipation effect does not change much. It is similar to the double-layer counter-impact energy dissipation valve with an outer diameter of 2000mm. After the water flows through the circular hole of the inner valve core sleeve, the counter-impact energy dissipation effect between the water flows is slowed down. There are also vortices in the area between the inner and outer layers, which also have an energy dissipation effect. In the inner layer area, after the water flows out from the surrounding circular holes, it still forms counter-impact energy dissipation.

[0152] For the double-layer counter-impact energy dissipation valve with an inner diameter of 1200mm and an outer diameter of 1600mm, the diameter of the outer valve core sleeve remains unchanged, the distance between the two layers decreases, the inner diameter increases slightly, and the energy dissipation effect does not change much. It is similar to the double-layer counter-impact energy dissipation valve with an inner diameter of 1000mm. After the water flows through the circular hole of the inner valve core sleeve, the counter-impact energy dissipation effect between the water flows is slowed down. At the same time, there are also vortices in the area between the inner and outer layers, which also have an energy dissipation effect. In the inner layer area, after the water flows out from the surrounding circular holes, a counter-impact collision energy dissipation phenomenon is formed.

[0153] The double-layer counter-attack energy dissipation valve has an inner diameter of 600mm and an outer diameter of 1000mm. The outer valve core sleeve diameter is the original inner diameter, and the inner diameter is reduced to 600mm. The outer valve core sleeve diameter is reduced, and the flow area between the outer layer and the valve wall increases. The flow rate is low and stable. When the water flows through the circular hole of the outer valve core sleeve, the flow area decreases, and the flow rate suddenly increases. The flow rate is about 26m / s. After the water flows through the circular hole of the outer layer, it enters the area between the inner and outer layers. There is vortex energy dissipation. Then the water flows through the circular hole of the inner layer and enters the inner layer area. The counter-attack energy dissipation between the water flows is obvious. The vortex is more obvious in the inner valve core area. There are also vortices in the area between the inner and outer layers, which also play an energy dissipation role. In the inner layer area, after the water flows out of the circular holes around, a counter-attack collision energy dissipation phenomenon is formed.

[0154] From the above analysis, it can be seen that when the diameter of the inner valve core sleeve remains unchanged, changing the distance between the outer valve core and the inner valve core, that is, increasing the diameter of the outer valve core sleeve, has little effect on the energy dissipation effect of the energy dissipation valve; when the diameter of the outer valve core remains unchanged, changing the diameter of the inner valve core in a small range has little effect on the energy dissipation effect; but when the diameters of both the outer valve core and the inner valve core are reduced, the water flow counteraction effect in the inner layer is obvious and the energy dissipation effect is enhanced.

[0155] (III) Modeling results of energy dissipation valve under high pressure difference and low back pressure

[0156] Under the condition of high pressure difference and low back pressure, the flow field calculation of single-layer counter-pressure energy dissipation valve and double-layer counter-pressure energy dissipation valve is different. Under the same pressure boundary conditions and other settings at both ends, the flow rate of single-layer counter-pressure energy dissipation valve is 9.6m 3 / s, the flow rate of the double-layer counter-pressure energy dissipation valve is 9.3m 3 / s, the energy dissipation effects of the two valves are basically the same, and the flow conditions are basically the same. Through visual analysis: Under this condition, the single-layer counter-type energy dissipation valve has cavitation near the wall of the valve core circular hole, which is not conducive to the normal operation of the energy dissipation valve and is not suitable for this condition; compared with the single-layer counter-type energy dissipation valve, the double-layer counter-type energy dissipation valve of structure 1 has achieved the effect of energy dissipation and pressure reduction under this condition, but slight cavitation occurs in the valve body; the improved double-layer counter-type energy dissipation valve of structure 2 has achieved the effect of energy dissipation and pressure reduction under this condition, and no cavitation occurs in the valve body. Therefore, it can be concluded that under the condition of high pressure difference and low back pressure, the double-layer energy dissipation valve with improved structure is better than the single-layer energy dissipation valve.

Claims

1. A method for improving the structure of a high-pressure difference and low-back-pressure energy dissipation valve for water conservancy and hydropower, characterized in that: By establishing the flow and flow resistance characteristic model of the counter-type energy dissipation valve, the internal flow field of the energy dissipation valve is numerically simulated and analyzed from the hydraulic perspective of the energy dissipation valve based on Fluent software, the energy dissipation valve is physically modeled using Pro / E modeling software, and its grid is divided using ICEM CFD. The grid division adopts unstructured and structured grids. The internal flow field of the counter-type energy dissipation valve is modeled under low back pressure. The physical models of single-layer and double-layer counter-type energy dissipation valves are used to analyze the flow and flow resistance characteristics of the two forms of energy dissipation valves, and the flow field and energy dissipation characteristics of single-layer and double-layer energy dissipation valves are extracted. The opening and closing dynamic process of the double-layer energy dissipation valve is analyzed based on Pumplinx, and its flow change process is analyzed. The single-layer energy dissipation valve is modeled under high pressure difference and low back pressure conditions, and the circular hole wall of its flow field is analyzed to have cavitation; the double-layer counter-type structure is improved, and the energy dissipation and anti-cavitation performance of the double-layer improved structure are enhanced compared with the single-layer energy dissipation valve; A. Flow and flow resistance characteristic model of energy dissipation valve: The physical and flow domain model of DN2400 counter-impact energy dissipation valve is established through Pro / E, the flow domain model is meshed, static numerical modeling is performed on the meshed single-layer and double-layer DN2400 energy dissipation valve, and meshing is performed on the flow domain model of the double-layer counter-impact energy dissipation valve and dynamic numerical modeling of the valve opening and closing process is performed; Modeling and dynamic analysis of B energy dissipation valve: First, a static model is established: the flow of a single-layer energy dissipation valve changes linearly with the increase of the opening. When the water flows through the energy dissipation valve, a collision area is formed in the valve core sleeve. There is a vortex in the front end of the valve core sleeve, and a vortex is formed in the area near the pipe wall behind the valve. The collision and vortex area dissipate energy, and the high-speed flow area is concentrated in the center of the valve core sleeve; the flow of a double-layer energy dissipation valve gradually slows down with the increase of the opening. After passing through the double-layer valve core and throttling twice with circular holes, the water flows in the inner layer of the valve core to form a collision energy dissipation, and then forms a central area flow velocity zone to flow downstream. The double-layer energy dissipation valve is more evenly distributed than the single-layer flow field at each opening, and the maximum flow rate is small; second, a dynamic model is established: during the closing and opening process of the double-layer energy dissipation valve, the flow through the valve changes linearly in a step-like manner with the increase of the opening, but the flow change rate gradually decreases; C Modeling improvement of energy dissipation valve under high pressure difference and low back pressure: The double-layer counter-pressure energy dissipation valve operates stably under high pressure difference and low back pressure conditions, and the cavitation problem of the single-layer energy dissipation valve under this condition is solved through structural improvement.

2. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1 is characterized in that: Energy dissipation valve flow regulation method: The net inflow fluid mass through a section of the pipeline fluid control surface in unit time is equal to the increase in the control volume containing the fluid mass. The continuity equation on the pressure pipeline is expressed as follows: ρ1=ρ1;v1A1=v2A2=Q=Constant Formula 1 In the above formula, A represents the cross-sectional area of ​​the water pipeline, v is the average flow velocity of the pipeline, and ρ represents the density, which is the volume flow rate of the fluid passing through the cross section per unit time m 3 / s, considering the energy loss, it can be expressed as follows: Where, subscript 1 is the section before the energy dissipation device valve, subscript 2 is the section after the energy dissipation device valve, v1 and v2 are the average velocity of the fluid flow at the section, in units of m / s and h f is the head loss between the two sections, unit is m, α is the correction coefficient of fluid kinetic energy; The pipe diameter and cross-sectional area before and after the energy dissipation valve are the same, so the flow rate before and after the energy dissipation valve is assumed to be v, and the energy loss of the incompressible viscous fluid after passing through the energy dissipation valve is expressed as: h f It can also be expressed as flow velocity and resistance coefficient, and its mathematical relationship is: Combined with the continuity equation v = Q / A, the flow equation of the energy dissipation valve is obtained as follows: Where the flow area A is in cm 2 , pressure before energy dissipation valve p1, pressure after energy dissipation valve p2, fluid density ρ, unit g / cm 3 , (p1-p2) is the pressure difference before and after the energy dissipation valve. When the flow area A of the energy dissipation valve is constant and the pressure difference (p1-p2) before and after the energy dissipation valve is unchanged, the flow rate Q increases as the resistance coefficient ξ decreases. The energy dissipation valve changes the valve resistance coefficient by changing the opening and layout to achieve energy dissipation and flow regulation.

3. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1, characterized in that: Characteristic factor of energy dissipation valve: Based on the flow coefficient, let: get: N is a dimensionless coefficient. In the International System of Units (SI), the flow coefficient K is v It is defined as: the flow rate of water at room temperature passing through the energy dissipation valve within 1 hour under a pressure difference of 0.1MPa; Q represents the flow rate of the energy dissipation valve, in m 3 / h, △P represents the inlet and outlet pressure difference, the unit is 0.1MPa, ρ=1; The flow resistance coefficient of the energy dissipation valve is a dimensionless quantity: in: h j =h w -h f , Q represents the flow rate through the valve, v represents the velocity of the fluid in the pipe, and h j Indicates the head loss through the valve, h w represents the total head loss, h f represents the head loss along the pipeline, λ represents the head loss coefficient along the pipeline, D represents the pipeline diameter, and L represents the distance between the valve and the pressure measuring tube.

4. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1 is characterized in that: Energy dissipation valve model performance prediction: 1- Single-layer flow characteristics and flow resistance coefficient: DN2400 single-layer valve core of the energy dissipation valve with 5 different openings, analyze the flow change law of the energy dissipation valve, obtain the flow and resistance coefficient of the single-layer energy dissipation valve at different openings, record the flow value, calculate the flow coefficient of the valve, and summarize the results; in the process of valve opening, the flow resistance coefficient is very large at the beginning, and the flow resistance coefficient is reduced to 290 when the opening is 0.

6. At the beginning, the flow resistance coefficient decreases rapidly. When the opening is large, the increase in the opening has little effect on the flow change. When fully opened, the flow resistance coefficient is still around 110. When fully opened, the energy dissipation effect of the energy dissipation valve is also more obvious; 2-Double-layer flow characteristics and flow resistance coefficient: The DN2400 counter-pressure energy dissipation valve is between the linear adjustment characteristics and the quick-opening adjustment characteristics during use. When the valve is opened, the flow through the counter-pressure energy dissipation valve increases linearly with the increase of the valve opening, but the flow changes greatly, which is close to the quick-opening flow characteristics; After the opening is 0.3, the flow rate no longer changes linearly with the valve opening, and as the opening increases, the flow rate changes less with the opening; After the opening reaches 0.4, the relative speed of flow change decreases significantly. The closer to the maximum opening, the smaller the change of flow with the opening. When it is close to full opening, the flow regulation ability is not as strong as when it is at a small opening. In the process of valve opening, the flow resistance coefficient is very large at the beginning of opening. When the opening is 0.6, the flow resistance coefficient is reduced to 161.

68. At the beginning of the valve opening process, the flow resistance coefficient of the valve decreases rapidly. After the opening reaches 0.6, the change of the flow resistance coefficient with the opening gradually decreases, that is, at a large opening, the increase in the opening has little effect on the flow change. When it is fully opened, the flow resistance coefficient is still around 113. When it is fully opened, the energy dissipation effect of the energy dissipation valve is more obvious.

5. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1, characterized in that: Establishment and parameter setting of the dynamic process model of the opening and closing of the energy dissipation valve: In Pro / E, the original model at 0.6 opening is modified, and the valve area is divided into four parts, namely, the part outside the internal valve core movement valve out, the internal valve core movement part valve mid, the front area of ​​the inner valve core movement valve up and the rear area of ​​the inner valve core movement valve down. Then, the valve model with divided areas is saved as .stl file type, and the four parts are exported separately to obtain the physical model for dynamic simulation; Import the obtained double-layer opposed energy dissipation valve .stl type physical model into Pumplinx, and then divide and name the faces of each area in Pumplinx, use the Split by Angle item in Split / Combine Geometry or Grid, and use appropriate angles to divide the faces of each area separately, so that the faces of each area are divided into the required faces, and other unnecessary faces are appropriately merged. After the required faces of each area are obtained, each area is meshed separately; Mesh setting of the inner valve core movement area: The mesh setting of the valve up area is divided under the spoolvalve model, and the cylinder, valve and end faces in the valve up are brought into the sliding valve model respectively, and then the mesh size is divided, and the minimum mesh is set to 0.0008; then set the mesh of the valve down area, and use the structured mesh TemplateMesh for division, and use the sliding valve module boundary setting in the subsequent boundary setting; then set the mesh division of the valve mid area, and use the general mesh division Mesher, the minimum grid is set to 0.0008, and the boundary conditions are set using the sliding valve module boundary conditions; the other static grids of the valve are also set using the General Mesher module, and the minimum grid size is also set to 0.0008; the inlet and outlet pipe sections are divided using the structured grid Template Mesh. Through the above settings, the volume grid and surface grid of each area are obtained; Set the interaction surface and boundary conditions of the regional grid body and the valve core motion parameters. The interaction surface settings are as follows: the contact surface between the inlet pipe and the inlet of the valve is set as an interaction surface, the contact surface between the outlet of the valve and the outlet pipe is set as an interaction surface, the end surface of the valve down is set as a contact surface with the static part of the valve, the cylinder surface of the spool valve, valve mid and valvedown is set as a contact surface with the static part of the valve, the end surface of the valve mid is set as an interaction surface with the valve surface of the valve down, and a certain pipe section is set before and after the valve inlet. The inlet of the inlet pipe section and the outlet of the outlet pipe section are set as pressure boundary conditions, and the pressure difference is about 1m head; the dynamic valve core is set as follows, the valve surface and cylinder surface of the valve down, valve mid and spool valve are set as the valve surface and cylinder surface of the sliding valve module respectively, and the valve down and spool The end surface of the valve is set to the end surface of the sliding valve module, and the other surfaces remain the default wall surfaces; the movement mode of the inner valve core is a dynamic process of uniform opening and closing with a speed of 0.068m / s, and the valve opening and closing time is 10s.

6. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1, characterized in that: Analysis of the dynamic process of energy dissipation valve opening: First, establish a physical model and import the physical model into Pumplinx; then divide the imported model into surfaces and import the sliding valve model; then mesh the divided model; finally, set the boundary conditions and set the movement mode of the valve core sleeve; The energy dissipation valve opens at a uniform speed of 0.068m / s. When the double-layer offset energy dissipation valve is closed, the pressure before the inner valve core is constant and the flow is zero; the pressure after the inner valve core is constant and the flow is 0. During the valve opening process, the water flow begins to move under the action of pressure. At the beginning, the movement of the water flow is unstable. At the beginning, the flow increases rapidly with time. As time goes by, the rate of increase of the flow rate slows down. The trend of valve flow rate change with time is also the trend of valve flow rate change with opening degree, that is, the process of opening each hole basically changes linearly, but as the opening degree increases, the rate of change of flow rate in the process of opening each hole slows down.

7. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1, characterized in that: Model construction and boundary condition setting of energy dissipation valve under high pressure difference and low back pressure: To achieve the effect of high pressure difference in energy dissipation effect of single-layer energy dissipation valve, the flow area of ​​energy dissipation valve must be reduced, effective throttling and counter-energy dissipation must be strengthened. The valve core sleeve diameter of single-layer energy dissipation valve is 1600mm, and the outer and outer valve core sleeve diameters of double-layer energy dissipation valve are 1600mm and 1000mm respectively. It is determined that the single-layer counter-energy dissipation valve is set to 50 circular holes with a diameter of 90mm as the flow area, divided into 5 The double-layer energy dissipation valve adopts 60 circular holes with a diameter of 90 mm in the outer layer, arranged in 5 rows, with 12 circular holes in each row, and 80 circular holes with a diameter of 90 mm in the inner layer, all arranged in 5 rows, with 16 circular holes in each row, and 60 circular holes with a diameter of 85 mm in the outer layer, arranged in 5 rows, with 12 circular holes in each row, and 90 circular holes with a diameter of 90 mm in the inner layer, all arranged in 5 rows, with 18 circular holes in each row; Use Pro / E to get the flow domain diagram of the two energy dissipation valves, then divide the grid in ICEM, and finally import the .mesh file into Fluent, then check whether the size scale of the model is in compliance, then set the turbulence model to the standard k-ε model, and then set the fluid medium to water, set the inlet and outlet of the two interface valve bodies, set the inlet of the inlet pipe and the outlet of the outlet pipe to pressure boundaries, the inlet pressure is the total pressure of about 100m head, and the outlet pressure is 5m head; the solution and discretization methods are set to the default settings, advanced steady-state calculation, do not add the cavitation model first, wait until the calculation is stable, and then add the cavitation model: first add the multiphase flow model, then add the gas-water fluid medium to the fluid medium, set the fluid water to the first phase, and set the second phase to the gas-water phase. There is a situation where the first phase is transformed into the second phase. The cavitation model is set to the default Schnerr-Sauer model, and the parameters under this model select the default settings.

8. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1, characterized in that: Calculation of flow field of single-layer and double-layer energy dissipation valves: After numerical simulation by Fluent, the results are imported into CFD-Post for post-processing. The results analysis includes: Under the condition of high pressure difference and low back pressure, that is, the back pressure is 5m head, and the pressure difference is 95m, the place where cavitation is prone to occur is near the circular hole. The flow area of ​​the single-layer energy dissipation valve is very small, resulting in a large flow velocity at the circular hole. The water flow has a large velocity head. The total head of low back pressure is constant, and the velocity head is large, resulting in a decrease in pressure head. When the pressure drops below the saturated vapor pressure of water at this temperature, liquid water will be converted into gaseous water, and cavitation will occur; To reduce the cavitation part in the double-layer structure 1, it is necessary to reduce the flow velocity of the circular hole, so the double-layer structure 2 is established, the inner layer flow area increases, the outer layer flow area decreases, and the overall energy dissipation effect is the same; The double-layer counter-impact energy dissipation valve with improved structure has a lower flow rate at the last row of circular holes in the inner valve core, and the pressure is above the vaporization pressure. The location with a higher flow rate in the improved structure of the energy dissipation valve appears at the circular holes in the outer valve core, and the back pressure of the circular holes in the outer valve core is relatively large, and there is no part where the pressure is lower than the vaporization pressure. At the same time, the energy dissipation capacity of the outer layer is improved, and there is a vortex in the area between the inner and outer layers, which improves the energy dissipation. After the water flows out of the circular holes on all sides in the inner layer area, counter-impact collision energy dissipation is formed; From single-layer to double-layer structure 1 and then to double-layer structure 2 energy dissipation valve, the cavitation in the valve body changes from cavitation to partial cavitation and then to no cavitation, and the position and size of the cavitation also change from cavitation at the position of the circular hole used to cavitation at the position of part of the circular hole and then to no cavitation. The pit cavitation capacity of the energy dissipation valve after structural improvement is improved, and it is suitable for working conditions with high pressure difference and low back pressure.

9. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1, characterized in that: Flow field calculation of double-layer energy dissipation valves with different structures: By designing double-layer energy dissipation valves with different structures, the effect of the valve core sleeve diameter and the distance between the sleeves on energy dissipation is compared when the flow area is the same, that is, the number and size of the valve core circular holes are the same; The structural design of the energy dissipation valve is as follows: the diameter of the outer valve core sleeve energy dissipation valve is the same as the diameter of the outer valve core sleeve of the energy dissipation valve, that is, the diameter is 1600mm, the diameter of the inner energy dissipation valve is changed to 1200mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers; the diameter of the inner energy dissipation valve is the same as the diameter of the above energy dissipation valve, that is, the diameter is 1600mm, the diameter of the valve core sleeve of the outer energy dissipation valve is changed to 2000mm and 2200mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers; the diameter of the outer energy dissipation valve is the same as the diameter of the inner valve core sleeve of the energy dissipation valve, that is, the diameter is 1000mm, the diameter of the inner energy dissipation valve is changed to 600mm, and the number and diameter of the circular holes are the same as the number of the inner and outer layers; Under the condition of high pressure difference and low back pressure, that is, the back pressure is 5m head and the pressure difference is 95m, the difference in flow field and energy dissipation is analyzed: when the diameter of the inner valve core sleeve remains unchanged, changing the distance between the outer valve core and the inner valve core, that is, increasing the diameter of the outer valve core sleeve, has little effect on the energy dissipation effect of the energy dissipation valve; when the diameter of the outer valve core remains unchanged, changing the diameter of the inner valve core in a small range has little effect on the energy dissipation effect; but when the diameters of both the outer valve core and the inner valve core are reduced, the water flow counter-impact effect in the inner layer is obvious and the energy dissipation effect is enhanced.

10. The method for improving the structure of a water conservancy and hydropower high pressure difference and low back pressure energy dissipation valve according to claim 1, characterized in that: Under the condition of high pressure difference and low back pressure, the flow field calculation of single-layer counter-pressure energy dissipation valve and double-layer counter-pressure energy dissipation valve is different. Under the same pressure boundary conditions and other settings at both ends, the flow rate of single-layer counter-pressure energy dissipation valve is 9.6m 3 / s, the flow rate of the double-layer counter-pressure energy dissipation valve is 9.3m 3 / s, the energy dissipation effects of the two valves are basically the same, and the flow conditions are basically the same. Under this condition, cavitation occurs near the wall of the circular hole of the valve core of the single-layer offset energy dissipation valve, which is not conducive to the normal operation of the energy dissipation valve and is not suitable for this condition; compared with the single-layer offset energy dissipation valve, the double-layer offset energy dissipation valve of structure 1 completes energy dissipation and pressure reduction under this condition, but slight cavitation occurs in the valve body; the improved double-layer offset energy dissipation valve of structure 2 completes energy dissipation and pressure reduction under this condition, and no cavitation occurs in the valve body. Under the condition of high pressure difference and low back pressure, the double-layer energy dissipation valve with improved structure is better than the single-layer energy dissipation valve.

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